Switched mode power supplies rely on their control feedback loop response and passive component filtering to suppress input and output noise. Generally, these feedback loops have their bandwidths restricted to about one-fifth to one-tenth of the switching frequency as a result of component performance restrictions. Accordingly, their response to input voltage fluctuations is much slower than their switching frequency. This slow response is detrimental to performance, as many switched mode power supplies require faster response when current sharing, for example, when configured with multiple paralleled supplies.
To improve accuracy and response time, several forms of current mode control can be utilized to provide pulse by pulse current control. For example, hysteretic current mode control meets some of these requirements by implementing a fixed relationship between maximum, minimum, and average inductor currents on a pulse by pulse basis. This control method maintains a volt-sec. balance within the inductor during continuous conduction operation. However, the varying pulse width of the “on” and “off” timing of the power supply switching results in varying operating frequencies. This causes difficulties for system designers who require current sharing between multiple supplies as well as interleaved operation. Output ripple filtering is also negatively impacted as the operating frequency of this type of control varies over a wide range.
Alternate systems and methods of stabilizing the operating frequency of a switched mode power supply are desired.